This invention relates to a microreactor with wall preparation for performing heterogeneous catalytic gas phase reactions on an industrial scale. The reactor is constructed in layers similar to a plate heat exchanger, with the chambers thus formed and stabilized and segmented by spacers representing reaction chambers and heat carrier chambers. The layer construction is calculated in size so that optimal conditions in terms of flow, heat and material transport, reaction kinetics, process reliability and structural stability exist for industrial use in tonnage-scale production.
Plate-type microreactors are in widespread use in industry in the most diverse applications. The construction of these stacked reactors is essentially similar and includes one or more central feed lines for educts or heat carrier fluids, from which substreams are tapped off and directed into the respective layer. After the individual streams have passed through a layer and the respective chemical or physical process step has taken place, they are brought together, material by material, in central discharge lines and fed to follow-up layers or directed out of the reactor.
Microplate reactors of the type previously mentioned are disclosed in US2002/0106311 and U.S. Pat. No. 5,534,328, in which a multiplicity of layers and layer sequences are described, some of which perform different functions, but there is no disclosure with regard to an optimized construction or process control construction for industrial use. This is a deficiency of these publications, particularly in respect of more extreme process conditions such as high pressures, high temperatures and/or severely exothermal reactions or explosive gas mixes.
In DE 39 26 466 there is a description of a microreactor for performing two-component chemical reactions whose use for reactions with severe heat of reaction is cited and which is also suitable for heterogeneous catalytic reactions. In the layers are longitudinal grooves through which the reaction partner flows after the bringing together of essentially two media, while a cooling medium flows in turn in a follow-up layer. This cooling is arranged transverse to the reaction grooves and takes place according to DE 39 26 466 at the end of the longitudinal grooves through the layer wall or over the complete layer length. To bring about the heat carrier operations and the necessary compactness, wall thicknesses of less than 1000 μm are specified, thus ruling out the use of this reactor for more highly aggressive reactions under high pressures. Furthermore, catalyst materials are often used in industrial applications which do not come from the group of known catalytically active metals and cannot be used as a base material.
In DE 196 54 361 there is a description of a stack-type reactor which is used for chemical-catalytic processes, the catalyst being applied as a layer to the inner walls of the reaction channels. Alternating with the layers containing the reaction channels there are layers in which a heat carrier fluid is conveyed similar to the previously mentioned publications, with a fluid connection existing between layers of identical type. In DE 196 54 361 there is disclosed a very simple variant for flow control within the reactor, whereby the reaction fluid arriving from the previous layer is distributed by means of a transverse slot to the following reaction layer or the discharge channel. A disadvantage of this nearly direct forwarding is that only very minimal homogenization processes take place between the substreams of the individual channels, resulting in the risk that channels will be used with different levels of intensity on account of varying flow resistances due to production tolerances of the wall or catalyst surfaces and to accumulations of deposits on the internal surfaces in the course of the reaction. This gives rise to a worsening of the reaction, resulting in the increased formation of byproducts and derived products or to a greater proportion of non-reacted educt at the outlet. The publication contains no information on the reaction-specific calculation of dimensions for the various layers or channels.
EP 1 031 375 discloses a microreactor for performing reactions in horizontal chambers, which works in similar manner to the previously mentioned reactor, with forwarding of the fluid to the next layer or function stage by way of a rotationally symmetrical channel. The decisive aspect of the microreactor disclosed in EP 1 031 375 is that the seal between the plates is effected without additional sealant materials by means of integrated sealing zones, which are realized through a high-grade surface finish on both sides and correct contact pressure. Another feature mentioned is that diverse processes and syntheses can be put together as required because this microreactor's function modules are interconnected with easy to separate connections. Very high requirements on surface finishes in contact and inspection areas in industrial applications are certainly a critical point, and for reactions with very pronounced heat of reaction or alternating pressure there is insufficient security against leaks.
In EP 0 903 174 there is disclosed a microreactor for fluid phase reactions of organic compounds using peroxides as oxidation agent, which solves the problem of reliable temperature control over an alternating and stack-wise sequence of reaction and cooling layers, whereby the microchannels of the neighboring layer always extend at right angles to each other and there is a maximal residual wall thickness between the reaction channel and the adjoining cooling layer of 1000 μm and a maximal hydraulic diameter of the reaction channels of likewise 1000 μm. The central challenge facing the peroxide reactions cited in this publication is explosion protection. Hence the imperviousness of the system and the assurance that the reactants used are optimally mixed is a fundamental requirement to prevent areas with explosive peroxide concentrations, but EP 0 903 174 makes no disclosures in this connection except for calculating the size of the channel cross-sections. In the publication mentioned, explosion protection is considered solely from the perspective of reliable compliance with the temperature required and concentrations.
From DE 100 42 746 there is known a device and a method in which at least two fluid media react with each other, whereby a pourable or wall-adhering catalyst is present if required. The reaction takes place in the described reactor in flat, gap-shaped reaction chambers. In the plates forming these reaction chambers there are cavities or bores in which the heat carrier fluid is passed through. The basic idea of this reactor disclosed in DE 100 42 746 is a parallel and flat fluid-moving reaction chamber without any additional built-in parts, with single spacers in the edge zone ensuring the right gap between two panels. Microdimensions in the range from 50 to 5000 μm are set in one dimension only, namely in the gap width. A further central feature is the inherent safety of this reactor, as the small free diameter suppresses the flame propagation. This reactor is very promising in its basic idea, but in industrial use with the large flat gaps there are likely to be partial blockages of the reaction slots. Such partial blockages result from high-pressure differences between the reaction chamber and the heat carrier fluid or from thermally induced stresses, for example in process-related start-up or shut-down operations.
When the wall is coated with a catalytically active material it is also likely that the previously mentioned material movements and process-induced oscillations and vibrations will cause flaking, leading in turn to partial blockage. The many cavities in the plates are very elaborate to manufacture and also very difficult to check and clean. The possibility of co-directional or counter-directional flow through the reaction slots and heat carrier chambers, such as is required for many reactions, is not available.